The present invention relates to an audio-signal correction apparatus, an audio-signal correction method and an audio-signal correction program for improving a clipped audio signal waveform.
It is required for an audio reproduction apparatus to give listeners the feeling of being at a live performance and full impact of the live performance when reproducing music especially pop, which is achieved by raising the sound level of reproduced music, as already known.
However, there is the maximum for the magnitude of reproducible sound level while music is being recorded in storage media such as CDs and DVDs. This is because, for storage media such as CDs and DVDs, it is required for music data to be expressed with a sound level within the range from −1 (0x7FFF as data) to +1 (0x8000 as data) in the fixed decimal mode of 16 bits, with a constant value +1 or −1 for the sound level out of the range. If a large sound continues beyond a recordable sound level during recording in storage media such as CDs and DVDs, a phenomenon called clipping occurs, that is vowel breaking, sound distortion, much noise, etc. to sounds when reproduced.
It is known that a mixing engineer uses a limiter in sound mixing to make clipping unnoticeable. The sound mixing using a limiter, however, depends on the skill of a mixing engineer and hence an improvement is required from the technical point of view.
In order to meet such a requirement, a known correction method uses sampled data prestored with the number of pieces of consecutive scaled-out audio data (clipped audio data) and the degree of change in the sound level of audio data that precedes or follows the consecutive scaled-out audio data, in correction of audio data for making clipping unnoticeable.
The known correction method uses prestored sampled data in correction of audio data. Thus, it is not always the case that audio data are corrected so that the audio data match the tone of music to be reproduced. Therefore, listeners may feel that reproduced music is not realistic.
For the reason above, there is a demand for a technique to correct scaled-out audio data for making clipping unnoticeable so that corrected data match the tone of music to be reproduced.